Human Nature – Part V: Upright Posture, Great Big Brains and Only One Hand Ax

For a fossil to be designated a hominin there must be evidence of upright posture. However, any orthopedic surgeon can tell you that upright posture produces extreme vulnerability for injuries to the lower back (perennially among the top ER visits), hips and knees, so it is reasonable that the evolutionary advantages of such a costly adaptation must have been central to the functioning of the earliest hominins. For a group to begin to shift into a language that could productively coordinate its behavior, the sheer volume of information that was required to be simultaneously expressed and comprehended increased by many orders of magnitude. These creatures stood up to be in constant visual contact with one another’s facial and upper body gestural expressions in order to mutually fathom the evolving coordination of collective behaviors, in the same manner that a musical band continuously makes small adjustments to stay in sync.

The peoples of our own genus Homo arose some 2.5 million years ago. It is a fact that the Homo peoples’ stone tool industry spread not only in Africa but through the vastness of Eurasia, and particularly in need of an explanation is that, after the shape of the tool stabilized, it remained unchanged for 1 ½ million years. Clearly, part of the progression of the early tool industry involved widely dispersed genetically mediated manual dexterity and hand-eye coordination. Yet there can be no doubt that the actual method of stone tool construction was spread culturally—and there’s the rub. Darwin’s challenge was to construct a theory that contained the potential of dynamic change over time within apparently unchanging species; but the riddle of the hand ax is quite the opposite—why is there such stasis in usually rapidly changing cultural transmission? Darwin’s idea is that evolutionary change demands diversity in individuals, whereas the cultural evolution of the unchanging hand ax demands a unitary and unchanging cause.

The environment selecting these hand axes was the willfulness residing in a collective sphere, the unchanging functional essence of which was the maintenance of productively coordinated behavior. A central adaptive function of tool construction for the better part of two million years was not primarily their utility in butchering meat, or any of the other possible uses that have been hypothesized over the years, but as a ritual serving to maintain the foundation of the Homo peoples’ central advantage, which was the productive fecundity of their associations. Once the stone tool evolved into the perfection of the hand ax—bifaced, sized to fit the hand, heart-shaped, and sharpened all around the edges—there was no reason for it to evolve further.

And, finally, why, in the face of this glacial stasis in hand ax construction, did the later hominins evolve the world’s largest brains? For many years, a study by British evolutionary psychologist Robin Dunbar (1992) has been routinely cited as support for the idea that in primate species, the bigger the size of the species’ average group membership, the bigger the size of the brain. “Machiavellian intelligence” is a term used to describe the competitive ability to read an opponent’s mind, which, in a hierarchy, is informed by knowing everyone’s rank at any given moment. The bigger the group, the bigger the brain has to be to keep track of a large, fluid hierarchy.

However, when Dr. Dunbar began to study what correlated to large brain size in other animals, much to his initial dismay he found that the correlation was to monogamy and not group size. He characterizes the cognitively demanding behavior in monogamous pair-bonds as “active synchronization” (such as birds feeding their young) and then goes on to recognize that bonding is an “emotional experience” and that “language [and I would add science] is a notoriously poor medium for describing our inner emotional experiences.”

Beyond monogamy, it was the expansion of a communal decision-making process and the capacity for coordinated behavior (enabled by more high-quality nutrition from meat) that spurred the growth of the brain in the Homo peoples during the last two million years. The development of a communal mind could be characterized as maintaining its roots in a Freudian superego (justice), and then flowering into the collective unconscious that Carl Jung observed with its synchronicity and richness of shared symbols in the realm of communal thought.

So here is a peaceful vision of the evolution of our unique capacity for teamwork, but how can this Edenic vision be reconciled with our modern experience of constant war? To understand, we need to consider the evolutionary changes that resulted in modern humans in the next posting.

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"In this breathtakingly original book, John Wylie proposes a new theory of mind, one that reconciles evolutionary biology with psychodynamics. This is a great endeavor of the intellect and a deep review of consciousness itself."Andrew Solomon (Noonday Demon & Far from the Tree)